This single institution Phase I study of temozolomide will define the dose-limiting toxicity (DLT), maximum tolerated dose (MTD) and the pharmacokinetics of temozolomide when administered on a twice a day schedule (q 12hr) for 5 days. The primary objective is to characterize the safety profile and determine the DLT and MTD of temozolomide when given orally, to adult patients with advanced cancer. The secondary objectives are a) To characterize the pharmacokinetics of temozolomide when given twice a day (q12 hour) over 5 days, after a bolus dose of 200 mg/m2 to adult patients with advanced cancer b) To evaluate the biochemical modulary effect of temozolomide on the depletion of alkyltransferase (ATase) by measuring ATase levels in circulating peripheral blood lymphocytes and, at the MTD, in tumor biopsies c) To evaluate the antitumor activity of temozolomide when given twice a day (q 12 hour) over 5 days after a bolus dose of 200 mg/m2 to adult patients with advanced cancer. To date seven subjects have been enrolled.